The UN has warned that the Central African Republic is heading toward a humanitarian disaster, as people fleeing conflict pack into overcrowded camps with poor sanitation.
It says measles has broken out at the airport in the capital, Bangui, where about 100,000 people are seeking refuge from clashes between rival militias.
Separately, reports that the president is to step down have been denied.
Officials say that Michel Djotodia's resignation is not on the agenda.
President Djotodia's spokesman told the BBC that the president was on his way to neighbouring Chad to "attend a regional summit, but not to resign".
But the president's failure to quell violence between Christian and Muslim militias has prompted speculation that he may indeed step down at the summit.
"It's finished for him now," a source close to Mr Djotodia was quoted as telling Reuters.
A senior diplomatic source in Paris and political sources in Bangui told Reuters that regional leaders led by Chad had run out of patience with President Djotodia, who seized power in March as the head of Muslim Seleka rebels.
'Brink of catastrophe'
On Wednesday, the UN children's fund Unicef and other aid groups were racing to vaccinate 210,000 children displaced by violence in Bangui, after at least seven cases of measles - a potentially deadly disease - were confirmed.
The Unicef representative in CAR, Souleymane Diabate, said: "This is a deadly combination for children. Unless we act now, we could have a disaster on our hands."
France has deployed 1,600 troops to try to end the violence, but fighting has continued.
The African Union also has some 4,000 peacekeepers in the country.
The UN on Monday warned that the country was on the brink of a catastrophe.
About half the people of Bangui have been driven from their homes, a total of about 513,000, it said.
Mr Djotodia forced President Francois Bozize, who comes from the majority Christian population, to flee into exile.
The clashes have killed more than 1,000 people since December and the UN says 935,000 have been driven from their homes nationwide.
Some 2.2 million people are in need of humanitarian assistance.
Correspondents say that security for ordinary people has deteriorated sharply amid the inter-religious violence that began when the Seleka set off a wave of killing and looting in the majority Christian nation after seizing power.